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08/ZZ /9 5 1'Uh U9:51 rAA WOODWARD CLYDE 4017 , <br /> 3.0 ON -SITE VERSUS REGIONAL CONTROLS <br /> For the purposes of this memo, we will assume that all maintenance of the stormwater control <br /> system will be done by the City. From a maintenance perspective, the primary difference <br /> between a system of on -site versus regional controls is the number and size of facilities that <br /> must be inspected and maintained. An on -site system will generally have more, smaller <br /> facilities while a regional control system will have fewer, larger facilities. Because the total , <br /> cost depends on the number and type of facilities used, it is unclear whether an on -site system <br /> would be more expensive to maintain than a regional system, or vice versa. However, <br /> inspection costs generally increase with the number of facilities. Although maintenance costs <br /> are usually higher for a large regional control as compared with an on -site control, this can be <br /> offset by the fact that fewer regional controls are necessary. <br /> It is important to remember that the satisfactory performance of a stormwater control system, <br /> particularly with respect to water quality, requires that each facility is operating as designed <br /> and achieving optimal pollutant removal. Thus, the design and implementation of the <br /> maintenance program is as important in the success of the system as the selection or <br /> construction of the control facilities. <br /> REFERENCES <br /> City of Portland. 1995. Stormwater Quality Facilities: A Design Guidance Manual. Prepared <br /> by Woodward -Clyde Consultants. <br /> Washington State Department of Ecology. 1992. Stormwater Management Manual for the <br /> Puget Sound Basin. <br /> proj94A45042nahu1020Wsw+dW /malnac.doc 3 <br />